1. Field of the Invention
The present invention relates to a method and apparatus for cleaning an object such as a wafer using a brush.
2. Description of the Related Art
Manufacturing steps of a semiconductor or a thin-film head include a wafer cleaning step for removing contaminants on a wafer surface as necessary. Such wafer cleaning methods include scrub cleaning. Scrub cleaning is a method of removing deposits on a surface of an object such as a wafer by scrubbing the surface by a brush, applying the rotating brush to the object surface with a cleaning liquid.
Referring to FIG. 12, an example of a scrub cleaning process of related art will now be described. As shown, a wafer 111 as an object to clean is taken out of a loader bath 101 and supplied to a scrub cleaning apparatus 102.
FIG. 13 is a schematic front view of the scrub cleaning apparatus 102. FIG. 14 is a schematic side view of the scrub cleaning apparatus 102. As shown, the scrub cleaning apparatus 102 comprises: a rotating table (not shown); a cylindrical rotating brush 112 placed on the rotating table; and a cleaning liquid ejector 113 placed above the rotating brush 112 and having a plurality of cleaning liquid outlets arranged along the axial direction of the brush 112. For cleaning of the wafer 111 by the scrub cleaning apparatus 102, the wafer 111 is fixed on the rotating table. The rotating brush 112 is positioned so as to touch the surface of the wafer 111. A cleaning liquid 114 is ejected like a shower through the outlets of the cleaning liquid ejector 113 towards the rotating brush 112 and the wafer 111. In this state the wafer 111 is rotated by the rotating table and the rotating brush 112 is rotated. The surface of the wafer 111 is thereby cleaned. The cleaning liquid 114 is detergent or ultrapure water.
Next, as shown in FIG. 12, the wafer 111 is taken out of the scrub cleaning apparatus 102 and transferred to a spin dryer 103 where a rinse step is performed by megasonic rinse. The wafer 111 is then dried by the spin dryer 103. The wafer 111 is taken out of the spin dyer 103 and placed in a carrier 104 by an unloader.
Cleaning while applying a cleaning liquid in a spray to the rotating brush 112 has been generally performed as a scrub cleaning method of related art as described above. Another cleaning method is cleaning with an application of ultrasonic vibrations to cleaning water in a spray.
As disclosed in Japanese Patent Application Laid-on Hei 7-86218 (1995), another scrub cleaning method of related art is performing brush (scrub) cleaning and ultrasonic cleaning at the same time. That is, a cleaning apparatus having a cleaner with a desk-shaped brush and a cleaning liquid ejector placed near the brush is used. An object to clean is scrubbed with the brush while a cleaning liquid to which ultrasonic vibrations are applied is ejected through the cleaning liquid ejector.
In the related-art cleaning method described with reference to FIG. 12 to FIG. 14 and in the other related-art method disclosed in the above-mentioned publication, however, a very small portion of cleaning liquid layer is only formed on the object surface. Consequently, particles of contaminants removed from the object and abrasion residues of the brush are likely to be taken in the cleaning liquid on the object surface and to redeposit on the surface.
In the related-art method, a very small portion of cleaning liquid layer is only formed on the object surface as well when ultrasonic cleaning is performed at the same time by applying ultrasonic vibrations to the cleaning liquid. It is therefore difficult to achieve effects of ultrasonic cleaning as expected.